Asymmetric Organocatalytic β-Hydroxylation of α,β-Unsaturated Aldehydes

The first catalytic enantioselective β-hydroxylation of α,β-unsaturated aldehydes is presented. Using commercially available (E)-benzaldehyde oxime in the presence of 2-[bis(3,5-bis-trifluoromethyl-phenyl)trimethyl-silanyloxymethyl]pyrrolidine as organocatalyst, the corresponding chiral carbonyl β-oxime ethers are obtained in high yields and with excellent enantioselectivities. These optically active carbonyl and hydroxy β-oxime ethers are highly interesting biological compounds in, e.g., sex pheromone analogues, highly potent antiinflammatory agents, and penicillin and cephalosporin analogues. The chiral carbonyl β-oxime ethers can be reduced to the corresponding 1,3-diols in high yields. Furthermore, the organocatalytic enantioselective β-hydroxylation of α,β-unsaturated aldehydes could be performed on gram scale without loss of enantioselectivity.